This invention relates generally to formation of MRAM (magnetic random access memory) cells in a semiconductor device, and more particularly, to magnetic tunneling junction (MTJ) devices and methods of fabricating a bottom electrode for such a device, wherein the method and structure provides a bottom electrode having a flat surface coplanar to the dielectric.
The MTJ device is essentially a magnetic switch which permits or prevents the flow of spin-polarized tunneling electrons (i.e. the device has a low or a high resistance) through a very thin dielectric spacer layer formed between an upper and lower electrode. Because the tunneling is spin-polarized, the current depends upon the relative orientation of the magnetizations of magnetic layers above and below the spacer layer. One of the two magnetic layers (the pinned layer) in the MTJ has its magnetization fixed in direction, while the other layer (the free layer) has its magnetization free to move in response to an external switching stimulus. Planarity variations between the bottom electrode and the adjacent dielectric prior to fabrication of the MTJ devices can cause topography, which causes poor grain growth and defects in the deposited MTJ.